For example, there is a fuel system is equipped with an aircraft or a jet engine of an aircraft. The fuel system includes a constant-volume fuel pump that boosts the pressure of fuel to a pressure suitable for the jet engine and supplies the fuel discharged from the fuel pump to the jet engine.
In order to prevent cavitation in the fuel pump, the fuel system is provided with a centrifugal pump that boosts a pressure of fuel, which is supplied to the fuel pump, to an extent to which cavitation does not occur in the fuel pump.
In the related art, the fuel pump and the centrifugal pump are connected to the jet engine and boosting power is input thereto from the jet engine. That is, drive shafts of the fuel pump and the centrifugal pump are connected to a turbine shaft of the jet engine via an accessory gear box and the drive shafts rotate with power generated from the jet engine.
In the constant-volume fuel pump, a discharge flow rate varies depending on a speed of revolution of the drive shaft.
Though the fuel pump is driven by the jet engine, the driving speed of the engine is not always suitable to the fuel pump operation. Accordingly, the speed of revolution of rotary power input to the fuel pump depends on the output of the jet engine and normally ranges from 70% to 100% of the speed of revolution in a substantially rated operation. As a result, even when the fuel flow rate required for the jet engine side is small, fuel of a large flow rate is normally discharged from the fuel pump. Accordingly, the fuel system according to the related art is provided with a circulation flow channel including the fuel pump and a fuel control unit discharging fuel of only a flow rate required for the jet engine side from the circulation flow channel. In the fuel system according to the related art, fuel of a large flow rate discharged from the fuel pump circulates in the circulation flow channel and only a required amount of fuel thereof is supplied to the jet engine by the fuel control unit.
In the fuel system according to the related art, since an amount of fuel (extra fuel) equal to or greater than the flow rate required for the jet engine circulates, extra power is consumed. Therefore, recently, a configuration in which a drive system of a fuel pump is separated from a jet engine and an electric motor is connected to the fuel pump has been proposed as disclosed in Non Patent Document 1. According to this configuration, the speed of revolution of the fuel pump can be varied depending on the fuel flow rate required for the jet engine side and it is not necessary to cause extra fuel to circulate. As a result, it is possible to suppress extra power consumption to improve the efficiency of the jet engine. Since the fuel control unit or the accessory gear box is not necessary, it is possible to achieve a decrease in the weight of an aircraft body.